Conventionally, materials intended to receive water-based inks by the inkjet printing technique are obtained by coating different layers on a support. The absorber layer absorbs the liquid part of the water-based ink composition after imaging. Elimination of the liquid reduces the risk of ink migration to the surface. The ink fixing layer prevents any ink loss into the fibers of the paper base to obtain good color saturation while preventing excess ink that would promote the increase in size of the printing dots and reduce the image quality. The absorber layer and fixing layer can also constitute a single layer ensuring both functions. The protective layer is designed to ensure protection against fingerprints and the pressure marks of the printer feed rollers. Some of these layers have a hydrophilic binder base, such as poly(vinyl alcohol).
Coating technology is also used in the photographic field, where photographic materials are obtained by coating various hydrophilic binder-based layers onto a support, especially image-forming silver halide emulsion layers, but also protection layers, intermediate layers such as an antihalation layer, an antistatic layer, etc. Such arrangements are described in Research Disclosure, Item 38957, page 624, section XI (September 1996). Research Disclosure is a publication of K enneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ, United Kingdom.
The hydrophilic binder generally used in the photographic field is gelatin, known for its rapid setting properties after coating, which enables high-speed coating processes. Poly(vinyl alcohol) has the disadvantage of setting less rapidly than gelatin. Its use thus entails a reduction of the coating speed that does not enable either cost reductions or productivity increases.
There have been attempts to improve the setting properties of poly(vinyl alcohol), especially in order to be able to replace gelatin by poly(vinyl alcohol) or in order to be able to use conventional photographic material coating installations to produce materials for inkjet printing.
One solution to improve the setting properties of poly(vinyl alcohol) consisted in using hardeners. Thus, DHD (dihydroxydioxane) has been used as hardener to improve the physical properties of coating. However, not only can DHD present toxicity problems, but it is also not a rapid hardener. The results are thus not a good as predicted. Sodium tetraborate (borax) has also been used as a hardener. Such a compound, thanks to its borate anions, reacts as a dicomplexation reaction with the hydroxy groups of the hydrophilic binder, leading to the gelation of the hydrophilic binder via intra and interchained didiol complexes. As the dicomplexation reaction is very rapid, borax enables a coating with excellent setting properties to be obtained. However, as borax is very efficient, it is difficult to mix it with the hydrophilic binder before coating. Indeed, borax starts to react with the binder prior to coating, and strongly modifies the binder's viscosity, which causes it to gel before the coating of the required surface, resulting in a material having poor physical properties, the appearance of coating defects, or even the stopping of the coating by the blocking of the coating machine if the binder's viscosity becomes too high.
Therefore, there is a need for a new material intended for forming or printing images, comprising a hydrophilic binder-based layer, and its new manufacturing method, enabling the gelation process of said hydrophilic binder, such as poly(vinyl alcohol), to be optimized and better controlled in order to obtain a hydrophilic binder-based layer that is uniform and has good physical properties.